The invention relates to a writing implement having a dispensing device for writing liquid at the front end and a liquid reservoir at the rear end.
Writing implements operated with liquid ink or liquid color solution, such as, for example, writing, painting, drawing or marking implements, usually consist of a liquid reservoir for accommodating the ink or dye solution and an ink dispensing device via which the ink is dispensed little by little during writing. Consumers like pens in which the ink stock is visible. These are known as "free ink systems". In order to be able to see the amount of ink still available, at least part of the liquid reservoir in writing implements of this type consists of a transparent plastic. If particularly high requirements are made of transparency, polyester, polyamide or polystyrene are possible materials. However, owing to the excellent mechanical properties, transparent grades of polyolefins, in particular polypropylene, are increasingly also being used. Polypropylene is hydrophobic and repels hydrophilic liquids. If, therefore, use is made of a water-based ink, which generally has relatively high surface tension, an ink film forming on the walls of the reservoir tears open at least partly, so that the fill level is readily visible. If, however, use is made of writing liquids whose surface tension is low, for example solvent-based inks or water-based writing liquids containing emulsifiers, a film remains adhering to the walls of the liquid reservoir and does not allow the fill level to be seen at all or only with difficulty or after an extended time. This problem is particularly serious if an ink based on a lipophilic solvent is used in combination with a lipophilic plastic.
In order to solve this problem, it has already been proposed to coat the inside of a liquid reservoir with suitable hydrocarbons. However, this method is most suitable if emulsifier-free, water-based inks are used. It is unsuitable for solvent-based writing liquids as the hydrocarbon coating partly or completely dissolves. The coating is thus removed, and under certain circumstances the writing liquid is changed. Both are undesired.
Accordingly, it is a principle object of the invention to provide a writing implement in which the fill level of the writing liquid can be seen easily and rapidly. It is a further object of the invention to provide a coating for a liquid reservoir which allows a liquid film adhering to the surface rapidly runs off the inside surface. In accordance with the invention the coating must exert its action durably and must not change the writing liquid in a disadvantageous manner.